1. Field of the Invention
The present invention relates to a novel type of gripping and locking/unlocking system.
The main application targeted by the invention is the handling of nuclear materials specimen holders in a research nuclear reactor, to allow specimen holders to be inserted and extracted without any break in the containment with respect to the external surroundings.
Although it is described hereinafter with reference to the main application, the invention also applies to any application in which it is necessary to insert an inner tube into an outer tube and to lock the two together following insertion and, conversely, to unlock the tubes from one another before extracting the inner tube housed inside the outer tube.
For the sake of conciseness, throughout the present application, a specimen holder tube may be referred to as an “SH tube”, and an instrumentation holder tube may be referred to as an “IH tube”.
Throughout the present application, the terms “lower”, “upper”, “vertical”, “raising”, “lowering”, “underneath” and “top” are to be understood as meaning with reference to an outer tube positioned vertically and handling by the gripper member from the top of its upper end. Thus, during a handling operation that allows an inner tube to be inserted into an outer tube, the gripper member is lowered.
2. Prior Art
In order to test how materials and fuels subjected to thermal, neutron or even chemical stresses representative of full-scale operation in an industrial nuclear reactor behave, it is common practice to use research reactors, which are tools that are indispensable in the research and development of nuclear electric reactor systems.
These research nuclear reactors are also commonly known as irradiation reactors because they allow irradiation experiments to be performed on specimens of nuclear materials, such as nuclear fuels, in the pool near or in the reactor core.
In particular, the research reactor that will soon enter service in France, the Jules Horowitz reactor (JHR) will make it possible to study how nuclear fuels behave under various irradiation scenarios.
In order to perform irradiation experiments in irradiation reactors, irradiation devices are designed specifically according notably to the location to be dedicated to them within the core and or nearby in a zone in which an irradiating flux is concentrated.
In the JHR reactor, there is an irradiation device specifically designed for studying nuclear fuels and cladding materials for the fuel rods that house the nuclear fuels.
In order to handle specimens of nuclear materials in research nuclear reactors it is known practice to use by way of specimen holders a tube inside which a specimen, such as a column of nuclear fuel pellets, is housed.
More specifically, a specimen holder tube (SH tube) comprises several tubular portions of different cross section including the widened one of the upper portion, referred to hereinafter as the gripper head, via which the SH tube is gripped so that it can be handled. The specimen that is to be irradiated is itself placed in a portion of the SH tube that is distant from the gripper head, preferably at the opposite end therefrom, especially when the specimen is a column of irradiating fuel pellets. In the installed configuration for irradiation within the core or nearby, the portion of the SH tube in which the specimen is housed needs to be positioned in a zone subjected to the neutron flux, under the conditions required for the irradiation experiment (T°, environment, etc.).
In order to take measurements of the physical parameters associated with the specimens, provision is made for the SH tube to be inserted into a concentric blind tube referred to hereinafter as the instrumentation holder tube (IH tube) in which notably measurement sensors and a cooling system are housed. An IH tube is anchored to part of the irradiation device.
Furthermore, in order to meet safety objectives, it is necessary to ensure sealing between the SH tube which constitutes the inner tube, and the IH tube which constitutes the outer tube so as to form a containment barrier, because the coolant of the cooling system circulating between the IH and SH tubes at a high pressure, typically of at least 160 bar, must not be able to escape into the pool of the irradiation reactor. In other words, in the installed irradiation configuration, it is necessary for the SH tube to be locked and sealed inside the IH tube.
Thus, prior to performing an irradiation experiment, the handling of an SH tube entails gripping it with a gripper member, lowering the gripper member and the SH tube to insert the latter into an IH tube, locking these two, SH and IH, tubes together with sealing, and raising the gripper member on its own.
For the reverse operation, after an irradiation experiment has been performed, the handling of an SH tube housed inside the IH tube entails lowering the gripper member, gripping the SH tube using the gripper member, unlocking the SH tube from the IH tube then raising the gripper member with the SH tube.
Again, in order to meet the safety requirements, the gripping of the SH tube by the gripper member has to be performed with the grip locked.
In the field of the handling of nuclear materials or radioactive substances, it is known practice to use gripper systems (gripper assemblies) with gripper fingers with the grip of the fingers locked and to use hooks to lock/unlock containers or drums containing either nuclear materials or containers which themselves contain radioactive substances. The use of hooks as locking means is often favoured because these constitute a reliable solution that is also simple to produce, and notably involves few mechanical parts.
Mention may be made here of patent application FR 2 725 188 which describes a solution for attaching a lidded drum to a vessel door with inner seal, in order to extract radioactive objects, whereby the locking/unlocking of the lid with respect to the inner seal is performed using hooks that are pivot mounted in the inner seal and the drum is locked/unlocked with respect to the vessel using hooks referred to as bell cranks pivot mounted on the wall of the vessel. One major disadvantage with the solution described is that it in fact requires the fitting of two separate locking/unlocking systems, which increases the number of parts and therefore the risks of seizing. Furthermore, before the actual catching proper, the handling of the drum entails the use of a lift plate positioned underneath. Now, in the main application at which the invention is aimed, it is inconceivable to install any lifting device underneath the SH and IH tubes. Finally, full implementation of the solution described, i.e. for removing both the lid and the inner seal in order to expose the inside of the drum to the volume of the vessel, entails a great many handling operations and therefore a lengthy process time. Now, in the context of a research nuclear reactor, replacing an irradiated specimen with a new specimen without the risk of breaking the containment needs to be a simple and rapid operation so that the number of experiments that can be carried out with one and the same IH tube in a given period of time can be increased.
Patent application FR 2 906 638 for its part describes a container for transporting a receptacle containing a radioactive substance, in which the lid of the container is locked/unlocked with respect to the body of the container using hooks pivot mounted in the lid, it being possible for the pivoting of the hooks to be brought about either by lowering a magnetic grip onto the magnetized lid, or by pivoting a mechanical grip pivot mounted on the lid. The system for gripping hold of the lid either by magnetic means or using the mechanical grip as described in this application is not really conceivable in the context of a nuclear reactor.
There is therefore a need for a system for gripping hold of a specimen holder tube and for the sealed locking/unlocking of a specimen holder tube in an instrumentation holder tube within an irradiation nuclear reactor with the grip locked/unlocked, which is reliable, simple to produce with a limited number of parts, and quick to use.
More generally, there is a need for a system for gripping and locking/unlocking an inner tube in an outer tube concentric with the inner tube, with the grip locked/unlocked, which is notably reliable, simple to produce with a limited number of parts, and quick to use.